The stability of north and south slopes of the Three Gorges Project(TGP) permanent lock is very important to ensure safety operation of the lock. The problem has been paid close attention to by the domestic and foreign experts for a long time. For studying this problem, the authors chose the section 17 -  17 as a research section, which is one of the highest and the most complicated sections in geomorphologic and geologic conditions. Study procedures are: ① to analyze field observed results to find the change features and regularity of the slope; ② to compare the observed data with the computed results from FLAC program; ③ to establish two statistical models of north and south slopes so as to forecast the annually average increment of time -  effect from now to 2035. The research results show that, the slope is in stable, the predicted increment of time - effect is    very small, and the annually average increment will become small and small with    time  going -  on. So the deformation of time -  effect in slopes is considered to be stable.